Chapter 02 of 5
Inside a Night
Sleep cycles, REM and the strange world of dreams.
- Not One State
Sleep has stages
Sleep isn't a single state. Through the night, the brain moves through distinct stages with different patterns of activity.
- Cycles
About 90 minutes
Each sleep cycle lasts roughly 90 minutes, and most adults go through four to six cycles a night.
- Light Sleep
Drifting off
The first stage is light sleep. It's easy to wake from, and you may feel like you weren't asleep at all.
17 more cards in this chapter
Could you answer this?
During REM sleep, what happens to most of the body's muscles?
😴 The Science of Sleep
- 01Why We Sleep at AllWe spend a third of our lives asleep. Here's what it's for.
- 02Inside a NightSleep cycles, REM and the strange world of dreams.
- 03The Body's ClockThe inner timekeeper that runs your days — and the Nobel Prize that explained it.
- 0411 Days AwakeThe teenager who stayed awake for 264 hours — and what sleep loss does.
- 05Owls, Larks and Jet LagMorning people, night owls, and working with your own clock.